It's going to be harder to find new customers this late in the season, but they are out there. People who don't want to mow in the heat/humidity. People who aren't satisfied with their current LCO. People who just haven't started mowing yet.
If you want to get new clients right now, keep the free ads running on craigslist. Keep an attractive sign on your trailer gate and magnets on your truck. And ASK. People will not buy from you if you don't ask them to. Personally, I'd target an area I'd like to work and put door hangers out. There is all the work in the world available to all of us who want it.
You see an LCO loading up their equipment after a job...walk over with a couple of handfuls of ice cold bottled water and introduce yourself. Don't take up their time, but do throw out your business card and offer a cash incentive for any accounts they're willing to throw your way. Do the same with treatment companies. And when they do call you, get that cash in their hands that same day.